Prostate cancer is the most common malignancy in men and the second leading cause of cancer-related deaths. Traditional treatments have included radical prostatectomy and external-beam radiation therapy. Surgery has been the most common treatment because it is typically much more effective. Unfortunately prostatectomy is a major surgery that requires several days in the hospital and several months recuperation. As with all surgeries, there is a risk of complications, such as infection and uncontrolled bleeding. With prostatectomy, there is an additional risk of impotence or incontinence. Therefore, oncologists have sought alternatives.
Percutaneous prostate brachytherapy appears to be an ideal alternative to prostatectomy as a treatment for localized malignancies. It has already been effective in treating malignancies of other tissues, including cervix, breast, endometrium head and neck. In this procedure, radioactive pellets are deposited directly into the lesion through a long needle under visualization. Surrounding, healthy tissue is spared trauma from invasive surgery and radiation because the treatment is targeted. Moreover, brachytherapy is about as effective as prostatectomy without the long recuperation and risk of permanent side effects of surgery. Although brachytherapy is already recognized as an effective treatment for cancer, additional improvements are needed in areas such as isotope selection and dose and device design. For example, a problem would frequently occur when loading the needle with seeds and inserting the needle into the tissue. The seeds would prematurely exit the needle outside of the tissue or at inappropriate locations within the tissue.
In an effort to solve this problem, bone wax has been used to plug the end of the needle, and thus, prevent pellets from prematurely exiting the needle. Typically, about 0.05 cm is used, however, the amount can vary, which increases the uncertainty of the procedure. For example, in some cases the bone wax does not clear the needle tip, causing one or more seeds to be stuck within the cannula. In other cases, the pellet may stick to the wax at the tip of the needle, causing the pellet to be withdrawn with the needle.
The use of bone wax poses another significant disadvantage in that the wax is ultimately deposited into the tissue along with the pellets. Bone wax is not a tissue friendly substance because it is not absorbed by the body. Moreover, wax has been reported to aggravate existing infections and caused mild inflammatory reactions. As such, it is recommended by manufacturers that bone wax be used sparingly and that any excess bone wax should be removed from a surgical site. Furthermore, the long term ramifications of depositing bone wax into the body, especially the prostate, is not fully known. For example, introduction of a tissue irritant can result in fibrousing of the area, which may preclude the proper function of the urethra.
Another concern surrounding the use of bone wax, is that the wax causes the needle to be sticky and blunt. This decreases the needle's ability to pierce the prostate on contact. Consequently, as the needle is pressed forward against the prostate, the prostate moves forward several millimeters before the needle actually pierces the prostate. This movement of the prostate reduces the accuracy of intended pellet placement.
In an effort to solve the problem of controlling the exit of pellets from the needle, U.S. Pat. No. 5,810,769 to Schlegel and U.S. Pat. 5,281,197 to Arias disclose needles having a constricted portion, resulting in a narrowing of the hollow channel of the needle. The pellets are slightly larger in diameter than the narrowed portions of the needle, and therefore, the pellets are retained within the needle until they are forced through the narrowed portions. Although the constricted portions prevent the pellets from falling out and avoid the use of bone wax, the constrictions create a new set of disadvantages. As made clear by Schlegel, the pellets must have yielding or elastic properties to ensure that the pellets are not damaged. If the pellets are not elastic, the pellets may be damaged when forced through the constricted portion of the channel. A damaged pellet may result in the uncontrolled leaking of radioactive or medicinal substances from within the pellet. Another disadvantage of a needle having constricted portions is that the constrictions are not flexible, and therefore, the needle cannot accommodate a wide range of pellet sizes. If the pellets are too small, the pellets will slide right by the constricted portion, resulting in the pellets prematurely falling out of the distal end of the needle. On the other hand, if the pellets are too large, the physician may not be able to force the pellet beyond the constricted portions. Even if the large pellet is forced through the narrowed portion, the pellet may be seriously damaged in the process thereby lessening its effectiveness or safety within the tissue.
Another reference of interest is U.S. Pat. No. 4,105,030 to Kersco. The Kersco patent discloses a complicated gun-like, implant device for depositing multiple pellets. Kersco discloses a spring-activated retracting needle having a flexible finger at the distal tip. The flexible finger extends inward into the barrel of the needle, keeping the pellets retained in the needle until injection. After insertion of the needle into the target tissue, a spring mechanism retracts the needle from the tissue, leaving the pellets behind in the tissue. To be operable, the flexible finger located at the end of the barrel must be forced outward against the pressure of tissue and fluid as the needle is retracted. The device is incapable of depositing multiple pellets one at a time. More importantly, to the extent that the flexible finger can be forced outwardly into the tissue it may cause additional and unnecessary trauma.
Known systems designed to address the problem of pellets prematurely exiting the needle have done so only by creating a host of new problems. Therefore, a need has remained for a pellet implant device that can retain the pellets within the needle until ejection without the use of a wax, and that can individually inject multiple pellets of various sizes without causing unnecessary damage to the pellets or the tissue.